OpenGL Lighting support

In order to facilitate attractive 3D applications
As a user of Qt Quick 3D
I want to be able to use a variety of lighting options when rendering a scene.

Qt3D should support opengl lighting, including positional lights, multiple lights and spot lights. Positional and multiple lights are theoretically already supported, but are rendered unusable by bugs. Spot lights may also already be supported, but are untested.

Supported lighting options need bugfixes, tests, and examples.